5441336562
Table 3 shows the method proposed to assess the rock mass strength gives reasonable values of Mohr - Coulomb strength parameters. Using the GSI index the strength of a highly fractured clean rock is extremely high for both, disturbed (0=1) and undisturbed rock (0=0). A materiał with cohesion in the rangę of 0.61 to 1.17 Mpa can stand vertical between 90 to 170m with out considering the strength due to friction. It is unlikely a highly fractured rock can sustain a vertical slope with these heights.
6 CONCLUSION
A new approach is presented to assess the parameters mb, s and a in the Hoek - Brown failure criterion , The method uses the joint condition and fracture frequency via RQD and spacing as input to the criterion.
Two Rock Mass Classification systems are considered,; Bieniawski’s and Laubscher’s. Instead of using the overall Rock Mass Rating RMR derived using one of these systems as input to the strength criterion, two new parameters based on joint condition and fracturing of the rock mass Nf and Nc are used. These new parameters can be evaluated directly from the RMR and no new data is required .
The procedurę can address differences in joint condition and fracturing that are not reflected in the rating systems. The proposed method can differentiate between the strength of rock masses with high fracturing and clean rough joints and rock masses with Iow fracturing and smooth joints with gouge, even though they might have the same rock mass ratings.
REFERENCES
[1] Barton N R, Lien R, and Lunde J (1974) Engineering classification of rock masses for the design of tunnel support.
Rock Mech. 6(4), 189-239.
[2] Bieniawski Z T (1989) Engineering rock mass classifications, New York, Wiley
[3] Hoek E, (1983) Strength of jointed rock masses, 23,d Rankine Lecture, Geotechnique 33 (3), 187-223.
[4] Hoek E, Carranza-Torres C, Corkum B (2002) Hoek - Brown failure criterion 2002 Edition, Roclab program
Rocscience.
[5] Hoek E, Kaiser P K, Bawden W F (1995) Support of Underground Excavations in Hard Rock. Balkema
[6] Indraratna B, Wijewardena L S S, Balasubramaniam A S, (1993) Large - scalę triaxial testing of greywacke rockfill.
Geotechnique 43 (1), 37 - 51.
[7] Laubsher D H (1990) A geomechanics classification system for the rating of rock mass in minę design, J1 S Afr Inst
Min and Metal, Vol 90, No 10, pp257,273
[8] Rocscience (2004), Roclab program.
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